Oedaleonotus enigma (Scudder)
Wyoming Agricultural Experiment Station Bulletin 912
Species Fact Sheet
by Robert E. Pfadt
Geographic range of Oedaleonotus
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The valley grasshopper is a rangeland species, inhabiting the sagebrush-grass
and other semiarid associations of the west. Native host plants include
springparsley, balsamroot, big sagebrush, and rabbitbrush. The valley
grasshopper has found several introduced weeds to its liking: redstem
filaree, flixweed, and downy brome. The increase in number of favorable
food plants appears to be an important factor in outbreaks of the
species due to better nutrition. Abandoned farmland, Conservation
Reserve Program (CRP) land, and foothills of the California coastal
and Sierra Nevada ranges are especially favorable sites for development
of large populations.
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High densities of the valley grasshopper on rangeland cause severe
injury to forage plants. These grasshoppers are particularly damaging
to young grasses and legumes in newly reseeded rangeland. The species
has a high reproductive capacity. Density of adults may reach 20
per square yard and higher. Nymphs and adults in outbreak populations
often migrate into alfalfa, cotton, grains, and vegetables, causing
serious damage. The valley grasshopper may be beneficial at low
densities as it prefers weeds for food, thereby thinning and reducing
these strong competitors of valuable forage plants. No quantitative
study of damage or benefits of this grasshopper, however, has been
The sizes attained by adults from one population to another are
highly variable and are probably due to variations in environmental
factors among habitats, such as temperature and quality and supply
of food. Weights of adults collected in a drought-stricken habitat
12 miles south of Mountain Home, Idaho, and then caged and fed downy
brome for 11 days averaged 365 mg for live males and 530 mg for
live females (dry weight: males 110 mg, females 165 mg).
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The valley grasshopper is primarily a forb and shrub feeder, but
it also feeds to some extent on grasses. It has been observed to
feed heavily on introduced weeds that often grow abundantly in its
habitat. These include redstem filaree, tumble mustard, draba mustard,
pepperweed, and downy brome. It likewise feeds heavily on lichen.
In summer, when annual weeds have matured and dried, big sagebrush
becomes an important host plant. In abandoned fields and CRP fields
where big sagebrush no longer occurs, Russianthistle is often the
only green plant available to the valley grasshopper in mid-summer.
It does not feed upon this plant, but it does use it for roosting.
Adult grasshoppers have been observed nibbling on the leaves of
Russianthistle but never found to ingest any substantial amount
of the plant. This may indicate that other members of the goosefoot
family, including the sugar beet, are essentially immune to attack.
Under drought conditions the grasshoppers resort to feeding on ground
litter and dead or dying grasshoppers, and they will skirmish over
an apple core thrown on the ground.
Direct observations and examination of crop contents have provided
records of the valley grasshopper feeding on seven species of forbs,
four shrubs, two grasses, one sedge, and one lichen. This list of
food plants is undoubtedly incomplete.
To learn how the valley grasshopper attacks food plants, twigs
of miniature rose (variety Meiponal) bearing leaves and blooms were
transplanted 2 August 1991 in an abandoned field 12 miles south
of Mountain Home, Idaho. Except for Russianthistle, the field contained
only dry vegetation and ground litter. Shortly after being transplanted
in the morning, the rose began to attract the adult grasshoppers.
Some grasshoppers jumped onto the stem before making direct contact,
while others kept crawling until making contact and then began to
feed on lower leaves. In either case, individuals fed on the leaf
edge beginning at the base or at the tip and often consumed the
entire leaf before attacking another. A feeding grasshopper either
stood on the ground or held onto the plant with the midlegs and
hindlegs and used the front tarsi to hold the leaf and direct it
to the mouthparts. Some grasshoppers cut through the petiole of
leaves, which fell to the ground. Fallen leaves were eaten by grasshoppers
still crawling on the ground. The grasshoppers also fed on the bracts
and petals of flowers.
Valley grasshoppers were also offered transplanted spearmint. They
fed on this plant in essentially the same way as on rose. They were
observed walking to the mint and beginning to feed on the edge of
the leaf down to mid rib and beyond. They also climbed the plant
and began to feed. Grasshoppers on the rose and mint assumed various
orientations suited to their feeding on the edges of leaves. At
times they fed on the centers of leaves by folding them.
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Slow dispersal of older nymphs and adults occurs almost daily.
During an outbreak nymphs tend to migrate in concentrated bands
of 20 to 30 per square yard. The grasshoppers may move in one direction
while following or entering a draw with greener vegetation or they
may spread out in all directions. Populations are known to move
from abandoned fields and rangeland into irrigated crops.
Long-winged adults may disperse by flight. They are able to fly
from deteriorating habitats into more favorable areas. Evidence
for such flights comes from a drought-stricken habitat 12 miles
south of Mountain Home, Idaho. On 24 June 1991 a dense population
of young adults consisted of 54 percent macropterous and 46 percent
brachypterous individuals. Sixteen days later the population had
significantly decreased in density and consisted of only 18 percent
macropterous and 82 percent brachypterous, indicating emigration
out of the area by a majority of the long-winged adults.
Evasive flights of adults are straight, silent, and range from
4 to 8 feet in distance and 4 to 10 inches in height. On landing
they face directly or diagonally away from the intruder. Brachypterous
adults evade an intruder by jumping distances of 2 to 8 feet. The
larger, stronger adults jump farther than the smaller ones.
In spite of its importance to integrated pest management of destructive
populations, no special study of the dispersal and migration of
the valley grasshopper has been made. We do not know the length
nor height of flights, nor whether macropterous adults leave their
original habitat individually, in groups, or en masse.
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Figures 1-5. Appearance
of the nymphal instars, their sizes, structures, and color
patterns. Notice progressive development of wing pads. BL=body
length, FL=Hind Femur Length. AS=number of antennal segments
First Instar: BL 4-4.8 mm FL 2.4-2.7 mm AS 13.
Second Instar: BL 4.9 mm FL 3.2-3.3 mm AS 17.
Third Instar: BL 7.7-8.9 mm FL 4.4-4.9 mm AS 18-19.
Fourth Instar: BL 8.3-10.5 mm FL 6.1-6.5 mm AS
Fifth Instar: BL 12-15.5
mm FL 8.6-9.3 mm AS 22-24.
Figures 6-10. Appearance
of the sixth instar, adult male and female, cercus, and egg
Sixth Instar: BL 15-21.5 mm FL 9.5-11.7 mm
Adult Female: BL 17.5-21.5 mm FL 11-13.5 mm AS
Fig. 8, BL 19-24 mm
FL 11-15 mm AS 24-26.
Fig. 9, Side view
end of male abdomen showing shape of cercus.
Fig. 10, Egg pod and
The adult valley grasshopper is a large, colorful, spurthroated
grasshopper (Fig. 7 and 8). The tegmina range from short to long.
Short tegmina are as long or longer than the pronotum. Seven other
species of the genus Oedaleonotus can be distinguished by
their possession of tegmina shorter than the pronotum, and the tegmina
are usually narrow and widely separated. These seven species are
distributed mainly in California.
Valley grasshoppers with long tegmina also have long hindwings
that are functional organs of flight. Adults with short tegmina
have even shorter, nonfunctional hindwings.
The anterior edge of the pronotum has a narrow, conspicuously white
to cream-colored band, giving this grasshopper the appearance of
wearing a clergyman's collar.
The medial area of the hind femur is marked with fuscous chevrons
separated by light tan lines. The proximal end of the inner medial
area and the lower marginal area are colored orange. The hind tibiae
are blue. The cercus of the male is broad basally with apex abruptly
narrowed and fingerlike (Fig. 9).
Nymphs are identifiable by their color patterns, structures, and
shape (Fig. 1-6).
- Head. Face slightly slanting, vertex and occiput with fuscous
band down middle divided by narrow cream-colored line. Antennae
filiform, first two segments pale tan or yellow with several darker
spots, remainder of segments fuscous, each with narrow light ring
on anterior edge. Compound eye with many cream-colored spots in
brown reticulum, relatively large dark spot near center.
- Thorax. Disk of pronotum dark brown with longitudinal cream-colored,
narrow, fusiform band down middle. The entire dorsal light band
begins on head and extends onto abdomen becoming faint posteriorly.
- Hindleg. Medial area of hind femur with fuscous chevrons that
are broken in middle at proximal half; hind tibia light gray with
- General color light tan with fuscous spots and maculations.
Shape is robust, pronotum widens posteriorly, matching wide meso-
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Overwintering as eggs in an advanced embryonic stage, valley grasshoppers
hatch early in spring. Hatching may start in early April in California,
Nevada, and Idaho and continue for a month or longer. Hatching usually
occurs in the morning when air temperatures are between 45° and
90°F and soil temperatures are between 76° and 98°F.
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Upon hatching in early spring the nymphs usually have a plentiful
supply of food, but because of cool weather during this time of
year they develop slowly, becoming adults in about 42 to 50 days.
Compared with later-hatching species, the valley grasshopper has
a long nymphal period, due to both the cooler temperatures and to
the greater number of nymphal instars, six instead of the usual
five. The proportion of males to females is nearly 1:1. In different
years, the proportion of short-winged adults to long-winged adults
ranges from all short-winged to over 50 percent long-winged. Laboratory
tests indicate that temperature may be one factor that influences
this proportion. Cooler developmental temperatures (constant 80°F)
result in greater proportions of long-winged adults, while warmer
temperatures (constant 100°F) result in more short-winged adults.
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Although many adult valley grasshoppers disperse from their nymphal
habitats, variable numbers remain and reproduce, even in a deteriorating
habitat. In a north-central Nevada site in 1954 when average temperatures
were slightly above normal, the first adults appeared on 22 May,
mating pairs were noted 20 days later, and egg deposition began
two weeks after mating. Eggs begin development upon being laid in
summer; by fall they reach an advanced developmental stage (after
blastokinesis, stage 23), and then go into diapause. During winter
the diapause is broken and warming weather in spring enables the
eggs to complete embryonic development.
Females oviposit in bare ground adjacent to the base of shrubs
and weeds, under cover of low growing forbs, such as turkey mullein,
and around and under rocks. The pods, placed horizontally one-eighth
to one-quarter inch below the soil surface, contain 16 to 22 eggs
each. Anterior ends of the eggs face diagonally toward the soil
surface. On hatching, the nymphs emerge from the side of the pod
rather than through the end as is usually the case with other species
of grasshoppers. The pods are slightly curved, short, and wide -
one-half to five-eighths inch long and one-eighth to three-sixteenths
inch diameter. Eggs are olive tan and 4.8 to 5.2 mm long (Fig. 10).
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The valley grasshopper has the capacity to increase to high numbers
on rangeland and cause serious outbreaks. Densities may rise to
over 20 adults per square yard. Outbreaks may be terminated by drought.
At these times vegetation turns brown and desiccates, causing nutritional
problems for the grasshoppers. Older instars and adults may disperse
to survive in other areas with green host plants. Predation may
also effectively end an outbreak. During June of 1954 three species
of digger wasps (Tachysphex), which provision their offspring with
nymphs of the valley grasshopper, reduced a population in south
central Idaho from 25 per square yard to 3 per square yard. Large
numbers of wasps emerged in June 1955 but they had virtually no
grasshoppers on which to prey. Field studies indicate that the principal
dipterous parasite is the tangleveined fly, Neorhynchocephalus
sackenii (Williston); rate of parasitism during four years of
study was variable, ranging from 0 to 24 percent.
Regrettably, no population has been studied for more than three
years, a period too brief to gain useful information and insights
into the population ecology of this grasshopper. Important questions
for integrated management remain unanswered - how long outbreaks
last, how long populations remain at low densities, and how many
years are required for populations to grow from low to high numbers.
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The behavior of adults inhabiting a drought-stricken abandoned
field 12 miles south of Mountain Home, Idaho was observed for three
days in August 1991. Early food plants, tumble mustard and downy
brome, had matured and dried and only Russianthistle remained green.
Valley grasshoppers refused to eat this plant but regularly used
it for roosting.
The majority of valley grasshoppers spent the night roosting head-up
on the main or secondary stems of Russianthistle plants, but a small
number rested on the ground exposed or under a canopy of Russianthistle.
At daybreak, before the sun had risen, the adults were quietly resting
in different orientations. At this time (6 a.m. DST), surface soil
temperatures ranged from 52° to 64°F and air temperatures 1 inch
from the ground ranged from 52° to 62°F. An hour later the vertically
roosting grasshoppers assumed a basking orientation by adjusting
their position so that the sun's rays shone perpendicularly on their
sides. They remained quietly basking on the Russianthistle plants
for an hour, then began to climb down to the ground, head first,
where they again basked by turning a side perpendicularly to the
sun's rays and lowering the exposed hindleg to the ground. A few
spread this hindleg to the side, exposing even more of the abdomen.
Regular activities of pottering, feeding, and mating began at 8:30
a.m. when surface soil temperatures had risen to 82°F and air temperature
1 inch above ground level to 67°F. The grasshoppers fed on ground
litter and on dead or dying bigheaded grasshoppers, Aulocara
elliotti. By 10:45 a.m. ground temperatures rose to 110°F, inducing
grasshoppers to elevate their bodies off the soil surface by stilting
(raising up on their legs). By noon the soil surface temperature
was 130°F, and the majority of the grasshoppers had climbed or jumped
into Russianthistle, resting at heights of 4 to 7 inches. A few
crawled into the shade of Russianthistle and remained on the ground.
When temperatures moderated in late afternoon the grasshoppers again
became active pottering, feeding, and mating. By 8 p.m., an hour
before sunset, the majority of grasshoppers were roosting on Russianthistle
and remained in these positions for the night.
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Brusven, M. A. and J. D. Lamley. 1971. The food
habits and ecology of grasshoppers from southern Idaho rangeland.
Univ. Idaho in cooperation with USDA, Project Completion Report
Hostetter, D. L., S. L. Breeding, J. A. Onsager,
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Entomol. 34: 1-11.
Newton, R. C. 1956. Digger wasps, Tachysphex
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